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AGNT40 KWNM 271937
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
337 PM EDT Thu Apr 27 2017

.FORECAST DISCUSSION...Major features/winds/seas/significant
.weather for the North Atlantic Ocean W of 50W from 30N to 50N.

The latest GOES visible satellite imagery and the lightning
density product indicate an area of showers and isolated tstms
along a weakening cold front across the far outer waters in nrn
NT2. Ascat wind retrievals from 15Z indicated winds to 25 kt in
the southerly flow ahead of the front. Current surface observations
indicate up to 20 kt in the offshore waters, and the 12Z GFS
winds are initialized well when compared with the data. The
models agree in the short range, and all indicate that the front
will move east of the area early tonight while weakening. In
addition, the models all show another weak frontal boundary
currently inland extending south front the Great Lakes through
the Ohio valley into the Florida panhandle will move east tonight
before moving through the offshore waters Fri. The models have
only minor timing differences with the next front, and all
indicate it will weaken while moving into the area. Planning on
starting out with the 12Z GFS for the next forecast using 10m
winds in stable areas and first sigma winds in unstable areas.

Otherwise, the 12Z models remain in good overall agreement
throughout the remainder forecast period on the overall pattern,
although the 12Z GFS is faster than the 12Z ECMWF/UKMET with the
next frontal system on Mon. However, the 12Z agrees with the
timing of the GFS. In addition, the 12Z GFS/GEM are both showing
gales ahead of the associated cold front Mon night, though the
GEM extends them over the cold shelf waters where shallower
vertical mixing can be expected. The 12Z ECMWF/UKMET are both
weaker and indicate 25 kt with a small area of 30 kt. The ECMWF
is also weaker with the low level jet as the 12Z GFS indicates up
to 60 kt at 925 mb while the 12Z ECMWF indicates only about 50
kt. As a result, confidence with the gales on Mon remains below
average. Planning on following the 12Z ECMWF from 12Z Sat onward
and capping winds at 30 kt in next forecast.

Seas...The 12Z Wavewatch and ECMWF WAM have both initialized
within a ft of the current observations over the offshore waters.
The models are in good agreement over the forecast period.
Planning on using a 2 to 1 blend of the ECMWF WAM to Wavewatch
throughout the forecast period as a reflection the preferred
ECMWF winds.

.Extratropical Storm Surge Guidance...N/A.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Kells. Ocean Prediction Center.



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